Connect 3" NPSH straight hose thread to 3" NH fire hose thread (NST)

3-8NPSH and 3-6NH are both straight gasket-sealed hose threads at the same nominal size but to different standards (8 versus 6 threads per inch, 88.14 mm versus 92.02 mm major diameter), so their couplings do not interchange. A crossover adapter joins the two hose standards.

A shared nominal size hides a different pitch and diameter. Match the coupling to its own standard or use the crossover adapter; do not force one swivel onto the other.